Purpose:
Numerous population-based studies have found an association between obesity and ocular hypertension. The etiology is unknown but may be due to increased intra-abdominal pressure causing increased episcleral venous pressure and choroidal vascular congestion. We previously reported that obese patients had higher IOP compared to normal weight controls across different positions. This current study was to evaluate the effect of significant weight loss on IOP.

Methods:
This was a prospective cohort study enrolling 25 morbidly obese patients who participated in our previous study and were invited to return following bariatric surgery. Subjects had tonometry performed in 7 positions: sitting with the neck in neutral position, flexion at 30°, and extension at 30°, supine, right and left lateral decubitus, and with the head and upper body elevated at 30°. The order of measurements was randomized.

Results:
18 patients completed follow-up after bariatric surgery (mean = 17 months post-op). Mean weight loss was 49.1 kg, or 36% of total body weight. The mean IOP in the right eye was significantly lower following bariatric surgery in each position (mean difference 1.8±0.3 mmHg), except for the right eye in left lateral decubitus. There was no significant decrease in the IOP post surgery in the left eye, except for the supine head up position and in right lateral decubitus. Linear regression of percentage body weight lost and postoperative decrease in sitting IOP in the right eye demonstrated that every 10% body weight lost was correlated with 0.7 mmHg decrease in IOP (r2 = 0.21).

Conclusions:
We previously reported that obesity was associated with increased IOP compared to normal weight controls. Weight loss however was only weakly correlated with IOP lowering. Further studies are needed to elucidate the mechanism of increased IOP in obesity and whether other systemic factors, such as insulin resistance or blunted autonomic response, are at play.